This invention relates to a process and an apparatus for recovering nuclear fuel materials such as uranium oxide compounds from scrap materials containing such compounds.
The residue (herein generally called "scrap" or "scrap materials") from many nuclear fuel processing operations can be in various forms and contain a sufficiently high concentration of the nuclear fuel to justify its recovery. Generally, one of the preliminary steps in a nuclear fuel recovery process comprises calcining scrap materials to remove the volatile matter and then dissolving the soluble portion of the resulting calcine in an acid. Such a process has been conducted using a calciner and a slab-shaped leaching apparatus.
The prior art also includes dry processes for nuclear fuel recovery from scrap, with a representative process being disclosed in U.S. Pat. No. 3,578,419 in the name of Richard K. Welty and assigned to the same assignee as the present invention. This patent discloses a process for recovering hard scrap nuclear reactor fuel material in which the scrap is first oxidized in a fluidized bed and then comminuted, after which the oxidized material is reduced back to the original chemical form prior to the oxidation step with improved sintering characteristics.
The foregoing processes are not suitable for the efficient recovery of enriched nuclear fuel, such as uranium compounds, from filter media used to filter the air drawn from nuclear fuel processing operations. Typically, these filters (e.g., High Efficiency Particulate Air or HEPA filters) are made of fiberglass or include some fiberglass in the filter media. When incinerated, the fiberglass forms a clinker that can encapsulate the uranium and is insoluble in most commonly used acids.
In the past, ventilation filters have simply been disposed of by burial, or have been acid leached as a whole unit in a large tank. The leaching of filter media precludes complete recovery of the nuclear fuel and is, in addition, a manpower intensive operation that utilizes large volumes of acid.
Typically, the materials other than filter media containing small amounts of enriched nuclear fuel result from the processing of the enriched nuclear fuel into a form, commonly oxide or carbide, suitable for utilization in nuclear reactors. In greater detail, such materials are rags, uniforms, gloves, plastic, oils, etc. It has been found that when such materials are incinerated, they form chunks of various sizes that need to be comminuted or ground to a smaller uniform size in order to be efficiently leached in an acid solution. Accordingly, it has remained desirable to have a system for the efficient recovery of nuclear fuel materials from filter media, incinerator ash and other particulate materials.